Eugeneodontida
Eugeneodontida is an extinct and poorly known order of bizarre sharks. They possessed a unique "tooth-worl" on the symphysis of the lower jaw as well as pectoral fins supported by long radials. The palatoquadrate was either fused to the skull or reduced. It is possible that they may belong to Holocephali. Characteristics The tooth system of the Eugeneodontids varies widely, however, most have a parasymphysial tooth whorl. The upper maxillary teeth are displaced to the lower surface of the jaw. The body is spindle-shaped, with the sufficiently long tail section. Teeth Lateral teeth usually pressing, polyconic, in the form transverse numbers, different size for the elongation of jaw (for example, Caseodus and Fadenia have the largest according to the sizes teeth they are located approximately in the middle the branch of lower jaw). Sometimes, apparently, lateral teeth can be lost, as evidenced by the presence of individual fossil teeth being recovered. Tooth-whorl The position of the spiral tooth-whorl on symphysis is disputed by some scientists (there is, for example, the opinion that the spiral was fastened by some means in the region of throat, being the derivative of throaty teeth - it is more accurate, the kinks of the mucous membrane of throat, similar structures exist in bony fishes and primitive sharks). At the same time, fossilized skulls are known with the symphysial teeth clearly preserved in the same position that they would be when the creature was still alive. In some forms, probably, there are large symphysial arcs in both jaws. Gills Gill arcs are located behind the cerebral box, as in sharks, but their number is relatively small, five. Probably, in life, there were separate gill slots, however the presence of gill covers is not proven. Postcranial skeleton The Postcranial skeleton is known mostly by fossilized remains of Fadenia (Permian of Greenland), the exterior view of other representatives of group could be different. The free part of the metapterigiya goes all the way back to the limits of fin (structure as in many paleozoic sharks). There is one dorsal fin, located directly above the shoulder girdle. There are no abdominal and anal fins. The skeleton of Caseodus, a more poorly understood genus, is very similar in structure. Diet It is possible that these sharks fed on ammonites. Taxonomy Superfamilies * Caseodontoidea: Caseodontoidea includes the families Of Eugeneodontidae and Caseodontidae. They are characterized by the transverse- comb-like or inflated symphyseal teeth. A well-preserved fossil specimen, Fadenia from the Carboniferous and Permian of Greenland and North America, was a relatively middle-sized (about 1.5 meters in length) fish. *Superfamily Caseodontoidea **Genus Campodus **Genus Chiastodus **Family Caseodontidae ***Genus Caseodus ***Genus Erikodus ***Genus Fadenia ***Genus Ornithoprion ***Genus Romerodus **FamilyEugeneodontidae ***Genus Bobbodus ***Genus Eugeneodus ***Genus Gilliodus *Superfamily Edestoidea **Family Agassizodontidae ***Genus Agassizodus ***Genus Arpagodus ***Genus Campyloprion ***Genus Helicoprion ***Genus Parahelicoprion ***Genus Sarcoprion ***Genus Toxoprion **Family Edestidae ***Genus Edestus ***Genus Helicampodus ***Genus Listracanthus ***Genus Lestrodus ***Genus Metaxyacanthus ***Genus Parahelicampodus ***Genus Physonemus ***Genus Prospiraxis ***Genus Syntomodus External links *Palaeos Vertebrates 70.100 Chondrichthyes: Eugnathostomata at paleos.com *JSTOR: Journal of PaleontologyVol. 70, No. 1 (Jan., 1996), pp. 162-165 *More about Chondrichthyes at Denovian Times Category:Sharks Category:Eugeneodontida